Method of controlling a vehicle while operating under a cruise control

ABSTRACT

A method is provided for controlling a vehicle while operating under a cruise control so as to improve response to driver braking operation and shorten the free running distance by applying a preliminary braking force to a braking device when a preceding vehicle can no longer be recognized during preceding vehicle following control. Basically, the method includes: detecting a preceding vehicle and an inter-vehicle distance to the preceding vehicle from a host vehicle equipped with the vehicle driving control device; executing a preceding vehicle following control to control the inter-vehicle distance to the preceding vehicle towards a target inter-vehicle distance when the preceding vehicle has been recognized; and generating a preliminary braking force upon determination that no preceding vehicle can be recognized during the preceding vehicle following control performed in which the preceding vehicle was previously detected.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 11/033,837 filed on Jan. 13, 2005. The entire disclosure ofU.S. patent application Ser. No. 11/033,837 is hereby incorporatedherein by reference. Also this application claims priority to JapanesePatent Application No. 2004-039284. The entire disclosure of JapanesePatent Application No. 2004-039284 is hereby incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a method of controlling avehicle while operating under a cruise control. More specifically, thepresent invention relate to a method that generates preliminary brakingforce prior to the operation of the brakes by the driver, and improvesresponse to driver brake operation and shortens the free runningdistance.

2. Background Information

In recent years, many vehicles have been equipped with various automaticspeed control technologies. For example, an adaptive cruise controlsystem has been disclosed in U.S. Pat. No. 6,311,120 that is capable ofexecuting a following control function. In such an automatic speedcontrol device, when a host vehicle (an ACC vehicle) is traveling in afollowing control mode in which a host vehicle (an ACC vehicle) isautomatically follow a preceding vehicle, the automatic speed controldevice maintains the host vehicle's distance from the preceding vehicleat a desired inter-vehicle distance. In particular, the automatic speedcontrol device controls the host vehicle's speed so that the hostvehicle is automatically accelerated up to a preset vehicle speed, whenthe preceding vehicle itself changes its traffic lane and disappearsfrom the host vehicle's driving lane. On the other hand, when thepreceding vehicle actually exists ahead of the host vehicle but aninter-vehicle distance sensor, employed in the host vehicle, loses thetrack of the preceding vehicle owing to various factors, for example,curves, slopes, weather or the like, the device disclosed in JapaneseLaid-Open Patent Application No. 11-192858 maintains or holds the hostvehicle's speed at a vehicle speed given at the time when the precedingvehicle has been lost, until such time that the host vehicle reaches alost point where the preceding vehicle has been lost, so as to inhibitthe automatic accelerating mode from being initiated and to prevent thehost vehicle's distance from the preceding vehicle from being reducedinadvertently or undesirably.

There is also known a preliminary braking force control device thatgenerates a preliminary braking force prior to operation of the brakesby the driver, thereby improving response to brake operation by thedriver and shortening the free running distance. One such preliminarybraking force control device is disclosed in Japanese Laid-Open PatentApplication No. 2000-309257.

In view of the above, it will be apparent to those skilled in the artfrom this disclosure that there exists a need for an improved a methodof controlling a vehicle while operating under a cruise control. Thisinvention addresses this need in the art as well as other needs, whichwill become apparent to those skilled in the art from this disclosure.

SUMMARY OF THE INVENTION

So one problem that arises is that when the system of the host vehicleloses sight of a preceding vehicle during preceding vehicle followingcontrol, and then a preceding vehicle is again recognized, if thepreceding vehicle is decelerating, since no the preliminary brakingforce is being generated, response to brake application is low, and thehost vehicle ends up drawing close to the preceding vehicle.

It has been discovered that in the above-mentioned preliminary brakingforce control device, the preliminary braking force is generatedwhenever the distance between vehicles drops below a prescribeddistance, or whenever a target deceleration exceeds a set value. Thus, aproblem arises in that when the system of the host vehicle loses sightof a preceding vehicle during preceding vehicle following control, andthen the preceding vehicle is again recognized, and the precedingvehicle is decelerating. Since no the preliminary braking force is beinggenerated in the above-mentioned preliminary braking force controldevice, response to a brake operation is slow, and the host vehicle endsup drawing close to the preceding vehicle

In view of this problem, the present invention generates a preliminarybraking force in a braking device when a preceding vehicle can no longerbe recognized during preceding vehicle following control. In accordancewith one aspect of the present invention, a method is provided forcontrolling a vehicle while operating under a cruise control. Basically,the method includes: detecting a preceding vehicle and an inter-vehicledistance to the preceding vehicle from a host vehicle equipped with thevehicle driving control device; executing a preceding vehicle followingcontrol to control the inter-vehicle distance to the preceding vehicletowards a target inter-vehicle distance when the preceding vehicle hasbeen recognized; and generating a preliminary braking force upondetermination that no preceding vehicle can be recognized during thepreceding vehicle following control performed in which the precedingvehicle was previously detected.

These and other objects, features, aspects and advantages of the presentinvention will become apparent to those skilled in the art from thefollowing detailed description, which, taken in conjunction with theannexed drawings, discloses a preferred embodiment of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of thisoriginal disclosure:

FIG. 1 is a schematic structural diagram of a vehicle equipped with avehicle driving control device in accordance with one preferredembodiment of the present invention;

FIG. 2 is a control block diagram illustrating the functions of thedriving controller of the vehicle driving control device in accordancewith one preferred embodiment of the present invention;

FIG. 3 is a flowchart illustrating the driving control program executedby the vehicle driving control device in accordance with one preferredembodiment of the present invention;

FIG. 4A is a top plan view of a diagram illustrating how a precedingvehicle is lost from sight of a host vehicle after the preceding vehiclehas gone around a curve with a wall;

FIG. 4B is an elevational view of a view from the host vehicle in FIG.4A illustrating how a preceding vehicle is lost from sight of a hostvehicle after the preceding vehicle has gone around a curve with a wall;

FIG. 5 is an example of a preload cancellation determination map used bythe vehicle driving control device for determining if the preliminarybraking force should be cancelled;

FIG. 6 is a graph plotting the preliminary braking force versus targetacceleration;

FIG. 7 is a graph plotting the preliminary braking force versus radiusof curvature that is used for calculating the preliminary braking force;

FIG. 8 is a graph plotting the preliminary braking force versus downhillgrade that is used for calculating the preliminary braking force;

FIG. 9 is a graph plotting the fixation distance and fixation range ofthe driver that is used for calculating the preliminary braking force;and

FIG. 10 is a graph plotting the preliminary braking force versus howlong the driver has not been looking at the preceding vehicle that isused for calculating the preliminary braking force.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Selected embodiments of the present invention will now be explained withreference to the drawings. It will be apparent to those skilled in theart from this disclosure that the following descriptions of theembodiments of the present invention are provided for illustration onlyand not for the purpose of limiting the invention as defined by theappended claims and their equivalents.

Referring initially to FIG. 1, a host vehicle V_(H) is illustratedequipped with a vehicle driving control device in accordance with afirst embodiment of the present invention. The vehicle driving controldevice is configured with a preceding vehicle following control thatincludes one or all of functions of a so-called adaptive cruise control(ACC). The phrase “preceding vehicle following control” as used hereinrefers to performing inter-vehicle distance control and performingvehicle speed control so that an inter-vehicle distance will besubstantially maintained to a prescribed or set target value when apreceding vehicle is determined to be present in front of the hostvehicle V_(H), and so that the vehicle speed be substantially maintainedto a prescribed or set target value when no preceding vehicle ispresent.

As explained below, the vehicle driving control device of the presentinvention is configured and arranged to generate a preliminary brakingforce in a braking device when a preceding vehicle can no longer berecognized during preceding vehicle following control. The imparting ofpreliminary braking force referred to in the present inventionencompasses imparting a slight braking force that is nearlyimperceptible to the driver, as well as not actually imparting brakingforce, but shortening the free running distance, from the time thedriver applies the brakes, that is, from the time the driver steps onthe brake pedal, until a braking force is imparted, more than usual.More specifically, to use disc brakes as an example, in the former caseabove, this refers to a state in which the brake pads touch the discsand squeeze with a very slight force, while in the latter case, thisrefers to a state in which the brake pads are stopped just at theinstant before touching the discs.

In addition to hydraulic braking devices, the braking device in thepresent invention also includes link-type braking devices that make useof wires or the like, and electric braking devices. Particularly in thecase of a hydraulic braking device, preliminary braking force is alsocalled “brake preload,” because the preliminary braking force is appliedby adjusting the hydraulic pressure.

This host vehicle V_(H) includes, among other things, an engine 1, anautomatic transmission 2, a propeller shaft 3, a final drive 4, a pairof rear drive wheels 5 a and 5 b, a pair of front driven wheels 6 a and6 b, and a plurality of disc brakes 7 a to 7 d. The engine 1 is aconventional internal combustion engine that acts as a main drivesource, which transmits a drive force to the drive wheels 5 a and 5 bthrough the automatic transmission 2, the propeller shaft 3, and thefinal drive 4 in a conventional manner. The wheels 6 a, 6 b, 5 a and 5 bare fitted with the disc brakes 7 a to 7 d, respectively.

The host vehicle V_(H) further includes, among other things, an enginecontroller 8, a driving controller 9, a transmission controller 10, abrake controller 11, an inter-vehicle distance sensor 12, a camera 13,an image processor 14, a vehicle speed sensor 15, an accelerator pedalsensor 16 and a plurality of adaptive cruise control inputs 17-22. Thevehicle driving control device in accordance with a first embodiment ofthe present invention preferably includes the components 8-22.

The engine controller 8, the driving controller 9, the transmissioncontroller 10 and the brake controller 11 are preferably part of one ormore microcomputers that are configured with control programs thatcontrol the host vehicle V_(H) as discussed below. These controllers 8,9, 10 and 11 also include other conventional components such as an inputinterface circuit, an output interface circuit, and storage devices suchas a ROM (Read Only Memory) device and a RAM (Random Access Memory)device. It will be apparent to those skilled in the art from thisdisclosure that the precise structure and algorithms for thesecontrollers 8, 9, 10 and 11 can be any combination of hardware andsoftware that will carry out the functions of the present invention. Inother words, “means plus function” clauses as utilized in thespecification and claims should include any structure or hardware and/oralgorithm or software that can be utilized to carry out the function ofthe “means plus function” clause.

The engine 1 is operatively coupled to the engine controller 8. Theengine controller 8 controls the torque and speed of the engine 1 bycontrolling the throttle valve opening, fuel injection, ignition timing,and so forth of the engine 1 according to a throttle valve openingcommand value θ* from the driving controller 9.

The transmission controller 10 controls the gear ratio of an automatictransmission 2 according to a shift command value Ts from the drivingcontroller 9.

The disc brakes 7 a to 7 d are operatively coupled to the brakecontroller 11. The brake controller 11 is configured to conductautomatic braking control when the driving controller 9 is conductingthe preceding vehicle following control of the adaptive cruise control.The brake controller 11 generates brake hydraulic pressure according toa brake pressure command value P* from the driving controller 9, andsupplies this pressure to the disc brakes 7 a to 7 d. The brakecontroller 11 also generates brake hydraulic pressure according to adepression amount of a brake pedal detected by the brake pedal sensor(not shown), and supplies this pressure to the disc brakes 7 a to 7 d.

The inter-vehicle distance sensor 12 is configured and arranged todetect the inter-vehicle distance L between the host vehicle V_(H) and apreceding vehicle. The inter-vehicle distance sensor 12 is preferablyprovided on the lower part of the vehicle body at the front of the hostvehicle V_(H). This inter-vehicle distance sensor 12 emits a laser beam,for example, receives the light reflected back from a preceding vehicle,and measures the inter-vehicle distance L between the host vehicle V_(H)and the preceding vehicle. The inter-vehicle distance sensor 11 also isconfigured and arranged to detect the position of a preceding vehicle soas to recognize the presence of a preceding vehicle in the host vehiclelane or an adjacent vehicle lane. A scanning or multi-beam type of alaser radar device, a milliwave device, or the like can be used for theinter-vehicle distance sensor 12.

The camera 13 is configured and arranged to obtain images of an areaahead of the host vehicle V_(H). The camera 13 is provided at a lateralcenter portion of the host vehicle V_(H) such as at the top of thewindshield inside the passenger compartment. This camera 12 can be a CCDcamera, a CMOS camera, or the like.

The image processor 14 is configured and arranged to process the imagestaken by the camera 13. The image processor 14 is further configured andarranged to detect information about what is ahead of the vehicle, suchas road information (e.g., white lines on the road, road slope, roadcurvature, etc.), and/or preceding vehicle information (e.g., precedingvehicle velocity, preceding vehicle acceleration, preceding vehicledisplacement, etc.).

The vehicle speed sensor 15 is configured and arranged to detect thevehicle speed V that based on the rotational output provided on theoutput side of the automatic transmission 2. The driving controller 9detects the acceleration a of the host vehicle V_(H) by differentiatingthe vehicle speed V detected by the vehicle speed sensor 15.

The adaptive cruise control inputs 17-22 are various conventionalswitches or controls for performing the preceding vehicle followingcontrol. The adaptive cruise control inputs 17-22 are operativelyconnected to the driving controller 9. The main switch 17 is used forturning the preceding vehicle following control system on and off. Theset switch 18 is used for setting the desired vehicle speed. Theaccelerate switch 19 is used for increasing the set vehicle speed inunits of 5 km/h, for instance. The coast switch 20 is used for reducingthe set vehicle speed in units of 5 km/h, for instance. The cancelswitch 21 is used for canceling preceding vehicle following control. Theselector switch 22 is used for changing the set inter-vehicle distance.

and the presence or absence of a preceding vehicle detected by theinter-vehicle distance sensor 12,

When a preceding vehicle is present, the driving controller 9 performsinter-vehicle distance control to set the inter-vehicle distance Lbetween the host vehicle V_(H) and the preceding vehicle to the targetvalue L* based on the host vehicle speed V detected by the vehicle speedsensor 15, the inter-vehicle distance L and the presence or absence of apreceding vehicle detected by the inter-vehicle distance sensor 12 (apreceding vehicle detection section) the various forward roadinformation and/or preceding vehicle information detected by the imageprocessor 14, the set vehicle speed Vset set by the set switch 18, andso forth so. Thus, the inter-vehicle distance L between the host vehicleV_(H) and the preceding vehicle will be set to the target value L* whenthe vehicle is traveling at or below the set vehicle speed Vset. When nopreceding vehicle is present, the driving controller 9 performs vehiclespeed control so that the vehicle speed V will be to the set vehiclespeed Vset, such that the driving controller 14 outputs the acceleratorpedal opening command value θ* (the result of a control computation) tothe engine controller 8 and outputs the brake pressure command value P*(the result of a control computation) to the brake controller 11 toregulate the vehicle speed V.

FIG. 2 is a control block diagram illustrating the functions of thedriving controller 9. The driving controller 9 comprises a targetinter-vehicle distance setting component 31, an inter-vehicle distancecommand value computation component 32, a relative speed computationcomponent 33, a target vehicle speed computation component 34, and avehicle speed control component 35 (all in the form of software loadedinstalled in a microcomputer).

The target inter-vehicle distance setting component 31 is configured toset the target inter-vehicle distance L* according to the host vehiclespeed V by the following Equation (1).L*=V*T ₀ +L ₀  (1)

In Equation (1), the term “T₀” is the inter-vehicle time, while the term“L₀” is the inter-vehicle distance when the vehicles are stopped. Thetarget inter-vehicle distance L* can also be set according to thevehicle speed Vt of the preceding vehicle, rather than the host vehiclespeed V.

The inter-vehicle distance command value computation component 32 isconfigured to compute the inter-vehicle distance command value Lt whichis expresses as the change over time in the inter-vehicle distance untilthe inter-vehicle distance L reaches the target value L*. Morespecifically, the target inter-vehicle distance L* is subjected to alow-pass filter Ft(s) given by the following Equation (2), and theinter-vehicle distance command value Lt is computed.Ft(s)=ω²/(s ²+2ζωs+ω)  (2)

In Equation (2), the terms “ω” and “ζ” are a characteristic frequencyand an attenuation coefficient, respectively, for converting theresponse characteristics in the inter-vehicle distance control systeminto the targeted response characteristics. The term “s” is adifferentiation operator.

The relative speed computation component 33 is configured to compute therelative speed ΔV versus the preceding vehicle based on theinter-vehicle distance L from the preceding vehicle detected by theinter-vehicle distance sensor 12. More specifically, the inter-vehicledistance L is subjected to a bandpass filter Fd(s) given by thefollowing Equation (3), and the relative speed ΔV is computed.Fd(s)=ωc ² s/(s ²+2ζcωcs+ωc ²)  (3)

In Equation (3), term “ωc” is a characteristic frequency, term “ζc” isan attenuation coefficient, and these terms are determined by themagnitude of the noise component included in the inter-vehicle distanceL, and by the permissible fluctuation in short-period body longitudinalacceleration. The term “s” is a differentiation operator. The relativespeed ΔV can also be computed by subjecting the inter-vehicle distance Lto a high-pass filter instead of a bandpass filter.

The target vehicle speed computation component 34 is configured tocompute the target vehicle speed V* for matching the inter-vehicledistance L to the inter-vehicle distance command value Lt by using afeedback compensator. More specifically, the target vehicle speed V* iscomputed based on the relative speed ΔV and the inter-vehicle distance Lversus the preceding vehicle by the following Equation (4).V*=Vt−{fd(Lt−L)+fv*ΔV}  (4)

In Equation (4), term “fd” is the distance control gain, term “fv” isthe vehicle speed control gain, and term “Vt” is the preceding vehiclespeed (Vt=V+ΔV).

The vehicle speed control component 35 is configured to compute a targetbraking force F₀r for matching the vehicle speed V to the target vehiclespeed V* or the set vehicle speed Vset. The vehicle speed controlcomponent 35 is also configured to determine the throttle valve openingcommand value θ* the gear ratio command value Ts, and the brakingpressure command value P* based on the target braking force F₀r, andthen output the result to the engine controller 8, the transmissioncontroller 10, and the brake controller 11.

FIG. 3 is a flowchart illustrating the driving control program in afirst embodiment. This flowchart will be used to describe the operationin the first embodiment. The driving controller 9 executes th thedriving control program shown in FIG. 3 every 10 msec, for instance,when the main switch 17 of the adaptive cruise control inputs is turnedon.

In step S1, the various data needed for driving control is read by thedriving controller 9. This data includes, among other things theoperation status of the adaptive cruise control inputs or switches17-22, whether a preceding vehicle is present in the host vehicle laneand the inter-vehicle distance L as detected by the inter-vehicledistance sensor 12, preceding road information and/or preceding vehicleinformation detected by the camera 12 and the image processor 13, thevehicle speed V detected by the vehicle speed sensor 15, the amount ofaccelerator pedal operation detected by an accelerator pedal sensor 16,and so forth.

In step S2, the driving controller 9 determines whether or not precedingvehicle following control is in progress. If the main switch 17 is onand a preceding vehicle has been recognized, then inter-vehicle distancecontrol is performed so that the inter-vehicle distance L to thepreceding vehicle will be the target value L*. When preceding vehiclefollowing control is in progress, the program proceeds to step S3, butif preceding vehicle following control is not in progress, processing isconcluded.

In step S3, the driving controller 9 determines whether the system haslost sight of the preceding vehicle. In this embodiment, even though apreceding vehicle in the host vehicle lane is recognized by theinter-vehicle distance sensor 12, and the inter-vehicle distance L tothat preceding vehicle has been detected, if the preceding vehicle inthe host vehicle lane can suddenly no longer be recognized, and theinter-vehicle distance L cannot be detected, the driving controller 9determines that the system has lost sight of the preceding vehicle. Ifthe preceding vehicle has disappeared from sight, the program proceedsto step S4, and if a preceding vehicle can still be recognized,processing is concluded.

In step S4, the driving controller 9 determines whether or not thepreceding vehicle is no longer visible. A preceding vehicle may becomeinvisible when blocked by a building while crossing an intersection orgoing around a curve, or may become invisible upon cresting the top of ahill. Alternatively, a preceding vehicle may become invisible because ithas passed a parked vehicle ahead. FIG. 4A shows the situation when apreceding vehicle is blocked by a wall and cannot be seen from the hostvehicle V_(H) after going around a curve with a wall. FIG. 4B is theimage showing what is ahead of the host vehicle, taken by the camera 13,in the situation shown in FIG. 4A. The image processor 14 processes theimage taken by the camera 13, and detects whether a preceding vehicle ispresent in the image. Then the driving controller 9 determines from theprocessing by the image processor 14 whether or not the precedingvehicle has disappeared from sight. When a preceding vehicle that hadbeen detected up to that point vanishes from the image, the drivingcontroller 9 determines the preceding vehicle has disappeared fromsight.

Even if the inter-vehicle distance sensor 12 has lost sight of thepreceding vehicle, if the preceding vehicle can be detected by thecamera 13 and the image processor 14, then processing is concludedwithout generating a preliminary braking force. The camera 13 and theimage processor 14 assume the role of the driver's eyes, and there islittle need to generate a preliminary braking force when a precedingvehicle is present without the camera image, that is, the driver's fieldof vision, even if the inter-vehicle distance sensor 12 has lost sightof the preceding vehicle. A situation such as this can occur, forexample, when the host vehicle or the preceding vehicle makes a suddenlane change.

Meanwhile, when the inter-vehicle distance sensor 12 loses sight of thepreceding vehicle, and the camera 13 and the image processor 14 alsolose sight of the preceding vehicle, the program proceeds to step S5 inorder to generate a preliminary braking force. In step S5, thepreliminary braking force P_(p) is computed.

Then in step S6, an actuator is driven by the brake controller 11 togenerate the preliminary braking force P_(p). As a result, when apreceding vehicle that has disappeared from sight during precedingvehicle following control is discovered again, a braking force can begenerated without delay with respect to the brake operation by thedriver since the preliminary braking force has already been generated.Thus, the brakes 7 a to 7 d respond more quickly to braking operation sothat braking is improved and the free running distance is shortened evenif the discovered preceding vehicle is decelerating.

In step S7 after the preliminary braking force P_(p) has been applied,the driving controller 9 determines if an accelerate operation has beenperformed by using the accelerator pedal sensor 16 to detect if theaccelerator pedal has been depressed, or by detecting if the set vehiclespeed Vset has been increased with the accelerate switch 19. If anaccelerate operation has been performed, the program proceeds to stepS8, and an actuator is driven by the brake controller 11 to cancel thepreliminary braking force P_(p). This allows vehicle behavior to beobtained in accordance with the intentions of the driver. If in step S7,the driver has not performed an accelerator operation, the drivingcontroller 9 proceeds to step S9.

In step S9, the driving controller 9 determines if a preceding vehiclehas been re-recognized by the inter-vehicle distance sensor 12 or by thecamera 13 and the image processor 14, and if a preceding vehicle stillcannot be re-recognized, the program proceeds to step S5, and thegeneration of the preliminary braking force P_(p) is continued asdiscussed above.

On the other hand, if in step S9, a preceding vehicle has beenre-recognized, the program proceeds to step S10, where the drivingcontroller 9 determines whether or not preload can be canceled. In thisembodiment, whether or not preload is canceled is determined on thebasis of the inter-vehicle distance L and the relative speed Δv versusthe re-recognized preceding vehicle.

FIG. 5 is an example of a preliminary braking force cancellationdetermination map, produced from the relative speed Δv and theinter-vehicle distance L. In this two-dimensional map, in which thehorizontal axis is the relative speed Δv, while the vertical axis is theinter-vehicle distance L. When the host vehicle is moving faster thanthe preceding vehicle and is gaining on the preceding vehicle, thencancellation of the preliminary braking force is prohibited if the pointdetermined by the relative speed Δv and the inter-vehicle distance Lfalls within the shaded region of the preliminary braking forcecancellation determination map. That is, cancellation of the preliminarybraking force is prohibited when the relative speed Δv is higher and theinter-vehicle distance L is shorter. Conversely, even if the relativespeed Δv is high, then the cancellation of the preliminary braking forcewill be permitted if the inter-vehicle distance L is adequate.Consequently, when a re-recognized preceding vehicle is decelerating,the relative speed Δv will be high and the inter-vehicle distance L willbe short, so cancellation of the preliminary braking force isprohibited, and braking force can be generated without delay withrespect to the driver's operation of the brakes. Thus, the brakes 7 a to7 d respond more quickly to braking operation so that braking isimproved and the free running distance is shortened. Conversely, if theinter-vehicle distance L is sufficiently long, cancellation of thepreliminary braking force will be permitted, so normal preceding vehiclefollowing control can be performed.

If cancellation of the preliminary braking force was permitted in stepS10, the program proceeds to step S8, where an actuator is driven by thebrake controller 11 to cancel the preliminary braking force P_(p). Onthe other hand, if the cancellation of the preliminary braking force wasprohibited, the program proceeds to step S5 and the generation of thepreliminary braking force P_(p) is continued.

Methods for calculating the preliminary braking force P_(p) by thedriving controller 9 will now be described. The first calculation methodis one in which the preliminary braking force P_(p) is raised in inverseproportion to the target acceleration of the host vehicle. When apreceding vehicle is lost sight of, the host vehicle accelerates to theset vehicle speed Vset if the host vehicle speed V is lower than the setvehicle speed Vset. The target acceleration α* here is assumed to bedecided according to the vehicle speed when the preceding vehicle hasdisappeared from sight, for example, and is mapped out ahead of time. Asshown in FIG. 6, the preliminary braking force P_(p) is raised inproportion to the target acceleration α* during acceleration to the setvehicle speed Vset. Consequently, the preliminary braking force suitedto the difference in free running distance can be generated withoutdelay even if the acceleration of the host vehicle is high. The relationbetween the target acceleration α* and the preliminary braking forceP_(p) need not be linear as shown in FIG. 6.

The second calculation method involves raising the preliminary brakingforce P_(p) in inverse proportion to the radius of curvature of a curvedroad. The smaller is the radius of curvature of a curved road, thecloser the host vehicle has to be to a preceding vehicle to re-recognizea preceding vehicle that has gone out of sight. In a case such as this,if the preceding vehicle brakes and decelerates suddenly, the hostvehicle may get too close to the preceding vehicle and have to brakesuddenly as well. In view of this, as shown in FIG. 7, the preliminarybraking force P_(p) is raised in inverse proportion to the radius ofcurvature R of a curved road. As a result, when a preceding vehicle thathas disappeared from sight has been re-recognized, the braking forcecorresponding to the braking requirements can be generated withoutdelay. The relation between the radius of curvature R and thepreliminary braking force P_(p) need not be linear as shown in FIG. 7.The radius of curvature R of a curved road can be estimated from the yawrate or steering angle of the host vehicle, or can be estimated bydetecting a delineator disposed on the roadside, for example.

The third calculation method involves raising the preliminary brakingforce P_(p) in proportion to the downhill grade. When a precedingvehicle disappears from sight, the host vehicle accelerates to the setvehicle speed Vset if the host vehicle speed V is lower than the setvehicle speed Vset. Since speed response improves in proportion to thesteepness of the downhill grade, if a preceding vehicle that hasdisappeared from sight suddenly brakes and decelerates, the host vehiclemay get too close to the preceding vehicle and have to brake suddenly aswell. In view of this, as shown in FIG. 8, the preliminary braking forceP_(p) is raised in proportion to the downhill grade X. As a result, thepreliminary braking force P_(p) that is suited to the difference inacceleration result from the downhill grade X can be generated. Therelation between the downhill grade X and the preliminary braking forceP_(p) need not be linear as shown in FIG. 8. The downhill grade X can bedetected by a vehicle attitude detection sensor, or can be obtained asroad information from a navigation device, for example.

The fourth calculation method involves raising the preliminary brakingforce P_(p) in inverse proportion the attention being paid by the driverto the preceding vehicle. The fixation point of the driver is detected,and the fixation distance, fixation range, fixation frequency, etc., ofthe driver is detected as shown in FIG. 9. FIG. 9 shows the situationwhen the driver's fixation range is on a vehicle traveling in anadjacent lane, and the driver is not looking at the preceding vehicle inthe host vehicle lane.

The fixation point of the driver can be detected, for example, byprojecting infrared light onto the face of the driver, capturing animage of the driver's face with an infrared camera, subjecting thecaptured image to image processing such as digitization orcharacteristic feature extraction, and detecting the driver's nostrils,the inner and outer corners of the eye, the position of the pupil, andthe position of the reflection points generated at the cornea of theeyeball by projection of infrared light. Then, the direction in whichthe drivers' face is oriented is directed on the basis of thesedetection results, and the direction of the driver's line of sight isdetected on the basis of the corneal reflection points and the directionin which the driver's face is oriented. The fixation point in thedirection of the driver's line of sight is then detected on the basis ofthe positional relationship between the space inside and outside thevehicle and the driver's face (prestored in memory). The method fordetecting the fixation point of the driver is not limited to the methoddiscussed above.

Whether or not the driver was looking at the preceding vehicle beforethe driver lost sight of the preceding vehicle, and how long the driverhas been looking away from the vicinity of the preceding vehicle, aredetected on the basis of the driver's fixation point information andinformation such as a preceding vehicle and white lines ahead of thevehicle detected by the camera 13 and the image processor 14. If thedriver was not looking at the preceding vehicle just before thepreceding vehicle disappeared from sight, the preliminary braking forceP_(p) is raised by multiplying the preliminary braking force P_(p) by acoefficient K (such as 1.2). The preliminary braking force P_(p) canalso be raised in proportion to how long the driver was not looking atthe preceding vehicle before the preceding vehicle disappeared fromsight, as shown in FIG. 10.

When the attention of the driver with regard to the preceding vehiclehas decreased, it is more likely that a decision to apply the brakeswill be late, so the attention of the driver with regard to thepreceding vehicle is estimated from the driver's fixation pointinformation and the information about what is ahead of the vehicleprovided by the camera image, the preliminary braking force P_(p) israised in proportion to how much the driver's attention to the precedingvehicle is judged to have decreased because of looking to the side,etc., and a preliminary braking force that is suited to the delayeddecision to apply the brakes can be achieved.

In the embodiment discussed above, the preceding vehicle was consideredto have disappeared from sight when the inter-vehicle distance sensor 12lost sight of the preceding vehicle and no preceding vehicle could bedetected in the host vehicle lane by the camera 13 and the imageprocessor 14. This makes it possible to accurately determine that thepreceding vehicle has disappeared from sight, and the unnecessarygeneration of the preliminary braking force can be avoided. However,just the inter-vehicle distance sensor 12 can be used to detect that thepreceding vehicle has disappeared from sight, without installing theexpensive camera 13 and image processor 14, and this allows the deviceto be less expensive.

Also, a hydraulic braking device was used in the above embodiment, butthe present invention is not limited to a hydraulic braking device, andan electric braking device or a link-type braking device can be usedinstead. With an electric braking device, preliminary braking force canbe imparted by adjusting the current flowing to the electric motor.Electric braking devices have been disclosed in Japanese Laid-OpenPatent Applications H11-093991 and 2000-110860, for example, and thebraking devices disclosed in these patent documents can be applied tothe present invention. Also, with a link-type braking device in whichthe brake pedal and the brakes are linked with wires, for example, anactuator that drives the wires can be provided at some point along thelink, and the preliminary braking force imparted by controlling thedrive of this actuator. Furthermore, the braking device in the presentinvention may be either a disc brake or drum brake system.

In the illustrated embodiments, the constituent elements of the claimsand the constituent elements of the embodiments are in the followingcorresponding relationships. The inter-vehicle distance sensor 12constitutes the inter-vehicle distance detection section. The drivingcontroller 9 constitutes the preceding vehicle following controlsection. The driving controller 9 also constitutes the preliminarybraking force control section. The driving controller 9 also constitutesat least one of the radius of curvature estimation section, the downhillgrade detection section and the visual fixation point detection section.The driving controller 9 further constitutes the preceding vehiclefixation point determination section. The camera 13 and the imageprocessor 14 constitute the preceding vehicle detection section. Theaccelerator pedal sensor 16 and the accelerate switch 19 constitute theacceleration operation detection section. The various constituentelements are not limited to the above constitution, as long as thecharacteristic function of the present invention is not lost.

As used herein, the following directional terms “forward, rearward,above, downward, vertical, horizontal, below and transverse” as well asany other similar directional terms refer to those directions of avehicle equipped with the present invention. Accordingly, these terms,as utilized to describe the present invention should be interpretedrelative to a vehicle equipped with the present invention. The term“detect” as used herein to describe an operation or function carried outby a component, a section, a device or the like includes a component, asection, a device or the like that does not require physical detection,but rather includes determining or computing or the like to carry outthe operation or function. The term “configured” as used herein todescribe a component, section or part of a device includes hardwareand/or software that is constructed and/or programmed to carry out thedesired function. The terms of degree such as “substantially”, “about”and “approximately” as used herein mean a reasonable amount of deviationof the modified term such that the end result is not significantlychanged. For example, these terms can be construed as including adeviation of at least ±5% of the modified term if this deviation wouldnot negate the meaning of the word it modifies.

While only selected embodiments have been chosen to illustrate thepresent invention, it will be apparent to those skilled in the art fromthis disclosure that various changes and modifications can be madeherein without departing from the scope of the invention as defined inthe appended claims. Furthermore, the foregoing descriptions of theembodiments according to the present invention are provided forillustration only, and not for the purpose of limiting the invention asdefined by the appended claims and their equivalents. Thus, the scope ofthe invention is not limited to the disclosed embodiments.

1. A method of controlling a vehicle while operating under a cruisecontrol comprising: detecting a preceding vehicle and an inter-vehicledistance to the preceding vehicle from a host vehicle equipped with thevehicle driving control device; executing a preceding vehicle followingcontrol to control the inter-vehicle distance to the preceding vehicletowards a target inter-vehicle distance when the preceding vehicle hasbeen recognized; and generating a preliminary braking force upondetermination that no preceding vehicle can be recognized during thepreceding vehicle following control performed in which the precedingvehicle was previously detected.
 2. The method according to claim 1,further comprising controlling a host vehicle speed to a set vehiclespeed when the preceding vehicle can no longer be recognized by theinter-vehicle distance detection section, and increasing the preliminarybraking force in proportion to an acceleration when the host vehicleaccelerates to the set vehicle speed.
 3. The method according to claim1, further comprising estimating a radius of curvature of a road onwhich the host vehicle is traveling based on data indicative of a curvein the road; and increasing the preliminary braking force in inverseproportion to the radius of curvature that was estimated.
 4. The methodaccording to claim 1, further comprising detecting a downhill grade of adownhill road; and increasing the preliminary braking force inproportion to the downhill grade that was detected.
 5. The methodaccording to claim 1, further comprising detecting a visual fixationpoint of a driver; obtaining an image of an area ahead of the hostvehicle; processing the image to detecting a preceding vehicle position;determining if the driver was looking at the preceding vehicle positionbefore the preceding vehicle could no longer be recognized, based on ofthe visual fixation point of the driver that was detected and thepreceding vehicle position that was detected; and increasing thepreliminary braking force upon determining that the driver was notlooking at the preceding vehicle position before the preceding vehiclecould no longer be recognized.
 6. The method according to claim 1,further comprising obtaining an image of an area ahead of the hostvehicle; processing the image to detect the preceding vehicle in theimage; and generating the preliminary braking force when the precedingvehicle is no longer detected in the image and the preceding vehicle canno longer be recognized during execution of the preceding vehiclefollowing control.